Disco Clams’ Awesome Light Show

Party people, here’s your new patronus: the disco clam. A favorite of scuba divers, Ctenoides ales is known as the disco clam for its flashing light display that looks straight out of a dubstep show.

The marine world is rich with bioluminescent creatures that create their own light through chemical reactions. At first glance, it seems the disco clam is one of these. After all, disco clams hang out in dark parts of the ocean, have been found as deep as 50 meters (164 feet) below the ocean’s surface, and like deep crevasses. To find the clams, University of California-Berkeley researcher Lindsey Dougherty says she would “take a reef wall, look for place with holes, and dive in there, then look for smaller holes.”

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However, in a new paper in Journal of the Royal Society Interface, Dougherty and her colleagues report that disco clams aren’t bioluminescent after all. Rather, the clam’s tissues ripple and reflect light, causing a flashing illusion. But how are they reflecting light in places where there’s so little of it?

Dougherty found that the secret lies in disco clams’ tissues, which are red with a strip of white along the edge. Researchers were surprised to find that the white strip is made up of tiny silica spheres. Silica occurs very rarely in living things, and mostly in plants. It also turns out to be a great medium for the disco light job. It “works as a great [light] refractor because it’s highly reflective,” says Dougherty. “These are the only animals we’ve ever found that have nanospheres as a form of light scattering.

What’s more, Dougherty’s optical modeling found that the size of those silica nanospheres was nearly optimal for scattering light underwater. Ambient light has different wavelengths, and these frequencies are absorbed by water at different depths. Just 10 meters below the ocean’s surface, the environment loses longer-wavelength colors like red. Colors with short wavelengths, such as blue and green, prevail. The disco clam’s silica is most effective at reflecting light in blue-green environments.

Beyond looking cool, the disco clam’s display may serve a purpose. Dougherty and her colleagues are considering three possibilities. One is that the light wards off predators. Brightly marked marine species are often toxic, and while the disco clam isn’t, its flashiness mimics the brightness that predators typically avoid. Another hypothesis is that the clam’s light lures prey—the spider plankton and doe plankton clams eat may be attracted to light.

The light may also lure fellow clams for mating. Clams reproduce by releasing their eggs and sperm in the water at the same time, which mix and develop into larvae and baby clams, so the process works best if you have members of the opposite sex around you. Around 60 percent of the clams Dougherty found in Indonesia and Australia were in mixed-sex groups. You can tell the gender and age of clams from their size: Clams are born male and then mature into females, so small clams are young and male, while larger ones are older and female. The mixture of sizes suggests that the clams didn’t settle at the same time, and that the small male clams may have sought out places where they saw bigger female clams. “The chances they would end up there randomly is fairly low,” Dougherty says. She and her colleagues have counted at least 40 eyes on these clams (yes, clams have eyes, on the edges of their tissue). The researchers are running tests to see if clams can see other clams to make decisions about where to settle

With their ability to make the most of low light, disco clams may even inspire new technologies. Dougherty speculates that we may be able to mimic clams’ light-reflecting capabilities to create more efficient lighting in dim environments. At the very least, they’d make great set pieces on Skrillex’s next tour.